Preheat oven to 350°F. In a medium size bowl mix together the cookie crumbs, butter and sugar. Press into a 9-inch tart pan with a removable bottom. Bake until lightly golden and set, about 15 minutes. Set aside to cool.
To make the filling: In a medium-size mixing bowl mix together the sugar and lemon zest until fully combined.
Use a whisk or electric mixer on low speed to cream the butter with the lemon sugar. Add the whole eggs and yolk one at a time beating well after each addition. Add the lemon juice. Mix well.
Pour into a heavy bottomed saucepan. Simmer over medium-low heat until thickened to a pudding consistency about 10-15 minutes, stirring constantly to prevent scorching. Adjust the temp down, if needed.
Meanwhile, place 2 Tbsp cold water in a small bowl. Sprinkle gelatin on top; let stand until softened, about 5 minutes.
Remove lemon curd from heat and add softened gelatin. Mix well until gelatin is completely incorporated. Pour into baked tart shell. (See Cook's note)
Chill for 4 hours or overnight. Garnish with whipped cream and fresh berries.
For a completely smooth lemon curd strain through a fine mesh sieve to remove lemon zest.